the ips of ALL of your visitors are viewable within your server logs. There all kinds of "stats" plugins ..
as well as ..
I read your original post last night, and couldnt help but think that that you havent thought through whatever youre trying to accomplish though. Retroactively banning IPS isnt going to solve whatever security issues you think you have.. (I chose my words there on purpose, since youve not demonstrated that you were hacked-- password issues dont suggest anything other than the normal, repeatable password issues).
And even so, anyone thats behaving maliciously is going to be using a proxy IP, so banning the IP is a stop-gap measure, NOT a solution.
Last night, I couldnt get into the backend of my blog, kept on getting a password incorrect error, even though it definately was the right password.
If it hadnt been for the fact that they also joined my forum, I would not have been able to get the ip address.
again, learn to read your server logs.